Prevent Unjust Conviction for DWI or DUI Charges

by David J. Hanson, Ph.D.

We need to vigorously and strictly enforce laws regarding both DWI and DUI to increase public safety and reduce needless injuries and deaths. However, we must also be careful to prevent innocent drivers from being unjustly convicted if they are not in violation of the law.

Most lawyers, including those who sometimes defend those charged with driving while intoxicated or driving under the influence, don’t realize that alcohol breath tests (often called Breathalyzer tests) are, at best, only indirect estimates of a person’s actual blood alcohol concentration (BAC). As such, they are not accurate measures of actual BAC and unchallenged reliance on them leads to many unjust convictions of innocent drivers.

All alcohol breath testers are based on certain assumptions about human physiology. One of the most important such assumptions is that there is a constant ratio between the amount of alcohol in the blood and in the exhaled deep-lung breath called the blood/breath partition ratio. This ratio is generally assumed to be 1:2100. But this is only an average and the blood/breath partition ratio can vary from about 1:1500 to about 1:3000. The result is that the true BAC can be over-estimated by as much as .03 of BAC. For example, person with an actual BAC of .07 can register a falsely high BAC of .10. That’s the difference between innocence and apparent but convictable guilt.

Another important assumption involves the composition of the blood, specifically the hematocrit or solid particles suspended in the blood plasma. Alcohol is absorbed into the plasma but not the hematocrit. This means that if two otherwise identical people consume the exact same quantity of alcohol, the person with the higher hematocrit level (and, therefore, the lower proportion of plasma) will have a higher concentration of alcohol in the plasma, which will evaporate more quickly into the breath and register as a higher BAC. This means that people with higher hematocrit will receive falsely high BAC readings.

The average hematocrit for men is 47 (that is, their blood is 47% hematocrit), with a range of 42 to 52. Among women, the average hematocrit is 42, with a range of 37 to 47. In addition, an individual’s hematocrit can vary over time by as much as 15%.

Unfortunately, alcohol breath testers assume that every subject’s hematocrit is identical, regardless of gender of any other factor. Thus, for example, if a man’s actual hematocrit is 52 but the alcohol breath testing machine is based on the combined male and female average of 45, his reported BAC would be falsely high. In reality, his true BAC would be only 83% of the reported level. An apparently illegal BAC of .10 would actually be a very legal .08.

Alcohol breath testers also assume a human body temperature of 98.6 degrees Fahrenheit. Each degree of higher temperature will produce a 3.9% higher BAC test reading. The average body temperature of a healthy, normal person may be almost two degrees higher or lower than the assumed 98.6 degrees. In addition, a person’s body temperature may vary by as much as one degree over the course of a single day.

A human body under sufficient stress will generate a falsely high BAC reading. This is because stress increases blood flow in the lungs as well as its pressure.

Alcohol breath testing is also based on the assumption that it is conducted after alcohol absorption has ended. Absorption refers to the transfer of alcohol into the bloodstream. Research has found that readings taken during the absorption period consistently overstate the actual BAC. And they can do so by over 100% and sometimes as high as 230%.

Unfortunately, many states provide no requirements that would protect innocent drivers from unjust conviction. For example, at least two separate breath tests over time should be conducted to determine if absorption has been completed. Failing that or other safeguards against testing during absorption, drivers are at the mercy of chance rather than justice.

South Dakota is so concerned with the problem of false breath test readings that it does not accept them as evidence in any court case. Instead, it relies on the only true measure of BAC, which is based on analyzing a sample of a person’s blood.

Many alcohol breath testers are unable to distinguish between ethanol (beverage alcohol) and any of a number of naturally occurring substances in the breath, of which there are over 100.

In addition, many such devices can falsely identify camphor (often found in snuff and chewing tobacco); substances found in inhalers for asthma, including formoterol, salmeterol, salbutamol, budesonide and fluticasone; and substances found in aerosols, especially chlorofluorocarbons.

Many substances found in common products such as paints, paint thinners, petroleum products and cleaning solvents can cause false readings. These substances include ethylene, diethyl ether, acetonitrile, nitrous oxide, toluene, and isopropanol.

A number of medical conditions can lead to falsely high BAC readings. They include diabetes, acid reflux, hiatal hernia, and heartburn.

Non-medical factors can also lead to incorrectly high BAC readings, including burping, alcohol in the mouth, and food between the teeth.

In addition, a large number of problems associated with breath test machines can lead to false readings. Blood or vomit in the subject's mouth, electrical interference from cell phones and police radios, tobacco smoke, dirt, and moisture can all cause false readings. Other sources of error include such things as inadequate maintenance, inaccurate calibration, and incorrect use. The latter can occur because of inadequate training, careless procedures, ignoring error messages, etc.

There are easy ways to virtually eliminate being unjustly convicted of impaired driving. One way is choosing not to drink, another is maintaining a low BAC, and another is using a designated driver.

If you choose not to drink but find drinks forced on you, simply "lose" them or order such drinks as water, seltzer with a twist of lemon, orange juice, tomato juice, or other beverages that look like alcoholic drinks. You might even find that you enjoy yourself as much without becoming intoxicated. There's no hangover in the morning and it's also safer.

If you choose to maintain a low BAC, remember that the alcohol content of the typical bottle or can of beer, glass of wine, or liquor drink (mixed drink or straight liquor) is the same: about 6/10 ounce of pure alcohol. Eat food while consuming alcohol and pace your drinks to about one per hour.

Consider either using or being a designated driver. The non-drinking designated driver has a respected role at a social function where alcohol is served. There is no stigma to abstaining and serving as a designated driver can help legitimate a personal choice not to drink.

Breathalyzers are all unreliable to some degree and often lead to unjust fines, jail time, a criminal record, loss of employment, and other serious problems but you can virtually eliminate such problems if you choose not to drink, to maintain a low BAC, or to use a designated driver.